The present invention relates to a new and improved method of reducing the hardening distortion during the case hardening of large toothed gear rims or the like formed of steel, and further pertains to a novel support body member suitable for the practice of the inventive method.
By case hardening the teeth of toothed gear rims or ring gears or the like it is possible to appreciably increase the load limits--such as flank strength and tooth root or base strength--of gears and toothed rims. It is already known in this technology that, during case hardening of even smaller gears there arises a distortion on hardening, and that this distortion, with increasing size of the gears, causes even appreciably greater difficulties, since with increasing gear size the dimensional and shape changes progressively exceed the permissible tolerances. These dimensional and shape changes significantly increase the time which is needed for the subsequent grinding of the gear teeth. Therefore, it is desirable to maintain the hardening distortion, i.e. the dimensional and shape changes, associated with case hardening of particularly large toothed gear rims, within as narrow limits as possible.
When processing larger gears case hardened toothed gear rims are generally connected by means of wheel disks or webs formed of metal plating or sheet metal with their hubs or shafts, respectively; It is known from German Patent Publication No. 2,606,245, published Aug. 18, 1977, to weld the toothed rim formed of case hardened steel with the wheel disk, and to then weld such to the shaft or hub. The toothed or gear rim is subsequently provided with teeth and thereafter carburized and hardened. Already during carburization there can arise dimensional and shape changes to such a degree that the teeth must be post-machined prior to hardening. However, there thus are present at the gear teeth irregularities in the carburization or case hardening depth. During hardening there occur further shape and dimensional changes.
Additionally, by virtue of the different behavior in the dimensional changes of the differently welded components, namely the weld rim, webs formed of metal plating, and hubs for instance, there arise unpredictable internal stress conditions which, in conjunction with the welding seams, constitute a difficult to detect or control uncertainty or irregularity.
Therefore, it is preferable to carburize and harden as such the toothed or gear rim formed of case hardenable steel, and to only thereafter join such part together with a wheel disk or webs formed of metal plating or sheet metal.
During the carburization and subsequent hardening of a separate toothed or gear rim of appreciable size and having the usually modest wall thickness, there occur, however, large dimensional changes and distortions which, particularly in the case of small modules, render questionable the use of the toothed or gear rim following its thermal treatment.